1 files changed, 48 insertions, 0 deletions
diff --git a/common-util/src/main/kotlin/com/google/devtools/ksp/MemoizedSequence.kt b/common-util/src/main/kotlin/com/google/devtools/ksp/MemoizedSequence.kt
new file mode 100644
index 00000000..be7a05d6
--- /dev/null
+++ b/common-util/src/main/kotlin/com/google/devtools/ksp/MemoizedSequence.kt
@@ -0,0 +1,48 @@
+/*
+ * Copyright 2022 Google LLC
+ * Copyright 2010-2022 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.devtools.ksp
+
+// TODO: garbage collect underlying sequence after exhaust.
+class MemoizedSequence<T>(sequence: Sequence<T>) : Sequence<T> {
+
+    private val cache = arrayListOf<T>()
+
+    private val iter: Iterator<T> by lazy {
+        sequence.iterator()
+    }
+
+    private inner class CachedIterator() : Iterator<T> {
+        var idx = 0
+        override fun hasNext(): Boolean {
+            return idx < cache.size || iter.hasNext()
+        }
+
+        override fun next(): T {
+            if (idx == cache.size) {
+                cache.add(iter.next())
+            }
+            val value = cache[idx]
+            idx += 1
+            return value
+        }
+    }
+
+    override fun iterator(): Iterator<T> {
+        return CachedIterator()
+    }
+}